In movies humans fight off alien occupation forces, explode alien ships, and mind-control aliens with the power of love. How on earth can we think that would happen?

In Falling Skies, Noah Wyle is all set to fight off an alien invasion with the power of being a gosh darn nuisance. It's actually one of the more realistic takes on a way to stop occupation. What's unrealistic is the idea that occupation would occur in the first place. They'd just destroy us, and although it wouldn't be a fun ride, it would make for an interesting few hours of television. Instead, we have to watch good, old-fashioned earthling spunkiness take care of a vastly superior force.

One of the primary ways we stop an alien invasion in movies and television is by finding the alien's one big weakness. There's some hinting at that in Falling Skies. "These things can be hit," a gruff man with a gun says, "And they can be hit hard." They have a vulnerability. In Skyline — spoiler alert — it was true love. The problem with every such One Big Weakness is the audience starts picking apart why the key was that one weakness and no other.

In Signs it was water, but did it have to be fresh water? Wasn't it raining anywhere? Snow? And what about the water in the human body? Even though most of the body's water is suspended in cells, there's a lot of moisture left over. What happened to the aliens whose victims cried like a baby and wet themselves - as I most certainly would if I were being attacked by a clawed chameleon alien. Did those aliens die?

And what about the other people in Skyline? Did they not love anyone enough to take over their brain-eating alien hosts? The One Big Weakness is a tiny crack that is meant to end the movie happily but instead bursts it to pieces.

Sure, we're all happy to suspend our disbelief - with a crane if we have to - because laser fights and big alien ships are cool and we like to watch them. But any alien force so advanced that it can cross vast reaches of outer space would make short work of us. Remember, we're not just talking about technological advancement here. Space travel comes with a whole host of chemical, physical and biological challenges that have to be met.

How does this alien race combat bone loss, exposure to cosmic rays, cramped quarters on a ship, and perfectly recycling its waste while on board a space craft? If its technology allows it to shorten the voyage, how does it keep all outside contaminants out, and can it use that technology against us? If its tech forces it to take long voyages across space, how does it keep its immune system — and those of its offspring — going strong, and could it use that against us? An alien-invasion film might simply be a film in which every human on the planet dies within 24 hours, and just as the last person's eyes are closing in death - they see an alien ship land and an alien creature step out of it to plant a flag in the dirt. We may all be dead before we even know they're here.

When it comes to actual technology, we don't even have to consider. Independence Day is and shall remain an object of ridicule for saying that alien ships can be given a virus via a laptop, and that alien ships which can survive a nuclear attack can't put a shield on the one area of their ships vulnerable to a crop-duster. Any way you slice it, they have interstellar travel and we have iPads. There's not even a contest.

The biggest problem with most alien films is the assumption that they'd want anything that might keep us alive for even a second. There's a possiblity they'd want slaves, pack animals or meat, but what are the chances we'd be any good to them at all? Life is a light dust of carbon between an nitrogen-oxygen vapor and an iron core. Our biosphere would probably be a nuisance to them. It's hard to match complex biology. It's easy and profitable to harvest elements, though, and if they came across space, that very well might be what they were looking for. Perhaps the best, most realistic, movie that could be made about alien contact is the two hellish hours a small band of survivors of the initial strike would last as they saw the planet ripped apart and broken down under them.

The point is, if they don't want us alive, we won't be. We can fight and we can hack and we can find weaknesses and we can band together. We can do whatever we'd like. We'd still all be killed.